Flat Tube for a Heat Exchanger

ABSTRACT

The invention relates to a multi-channel flat tube ( 1 ) for a heat exchanger, especially for use in motor vehicles, which comprises a first lateral wall ( 14 ), a second lateral wall ( 15 ) substantially parallel to the first lateral wall ( 14 ), and at least one curved end section ( 17 ). A projection ( 9 ) from the material of the lateral wall ( 14, 15 ) is configured on at least one lateral wall ( 14, 15 ) on the inside facing a fluid flow in the interior of the flat tube ( 1 ). On the outside facing away from the fluid, the lateral wall ( 14, 15 ) is substantially planar in the area of the projection ( 9 ).

The present invention relates to a flat tube for a heat exchanger, in particular for a motor vehicle. According to the prior art, heat exchangers in motor vehicles, for example in automotive air conditioning systems, exhibit, in addition to collecting arrangements for a coolant, flat tubes that are provided for the purpose of the onward conveyance of the coolant and/or other fluids.

These flat tubes are connected in this case to the collecting arrangements via tube bases or the like. Particular importance must also be attached to the sealing in this connection.

The flat tubes previously disclosed according to the prior art exhibit ribs and/or projecting parts in their interior, the effect of which is for the flat tube as a whole to be of multi-channel execution.

The ribs previously disclosed according to the prior art consist of beads formed on both sides or ribs formed on one side. The flat tubes in this case do not, however, exhibit a closed and/or a smooth profile on their outside in the area of the ribs. The effect of this non-smooth external profile of the flat tubes is the need to incur a greater process expenditure in conjunction with the insertion of the flat tubes into the bases, in order to achieve a fluid-tight connection. Furthermore, according to the prior art, the ribs on the outside are not adequately closed, so that leaks arise in the connection between the tube and the base in the remaining external tube cavities. A remaining channel on the outside of the flat tube can also be the cause of failure in conjunction with soldering. In addition, according to the prior art, the external tube cavities occurring in the areas of the ribs must be recalibrated at the ends of the tubes after manufacture of the tubes, in order to achieve externally smooth tubes.

EP 0 854 343 illustrates flat tubes of this kind, which exhibit considerable external cavities on their outside, and these are reduced in size by an expensive process.

The object of the present invention is thus to make available a flat tube, which exhibits projecting parts in its interior and, at the same time, largely avoids depressions or recesses on its outside in the area of the projecting parts.

This is achieved according to the invention by a flat tube according to claim 1 and by a process for its manufacture according to claim 12. Preferred further developments of the flat tube and the process are the subject-matter of the dependent claims.

The multi-channel flat tube according to the invention for a heat exchanger, in particular for a motor vehicle, exhibits a first longitudinal wall, a second longitudinal wall, which lies substantially parallel to the first longitudinal wall, and at least one curved end section. In conjunction with this, a projecting part is configured on at least one longitudinal wall from the material of the longitudinal wall on the inside facing a fluid flow in the interior of the flat tube. According to the invention, the longitudinal wall is essentially level on its outside facing away from the fluid in the area of the projecting part.

The expression “multi-channel tube” is understood to denote that a plurality of channels that are essentially mutually separate from one another is configured in the inside of the tube. The expression “flat tube” is understood to denote a tube that is configured in its cross section in such a way that this exceeds one direction of extension by a good margin in a second direction of extension.

The expression “a longitudinal wall of the flat tube” is understood to denote the wall which runs along one of the longitudinal sides. The expression “a projecting part configured from the material of the longitudinal wall” is understood to denote a projecting part of a kind that is not subsequently applied to the wall, but—in particular, although not exclusively—is configured from the wall itself by a forming process.

The expression “in the area of the projecting part” is understood to denote the geometrical area of the corresponding longitudinal wall in which the projecting part is configured. The expression “essentially level” is understood to denote that the external profile in the area of the projecting parts does not exhibit any depressions, or that it only exhibits depressions with a small cross-sectional area.

In a further preferred embodiment, the projecting part is in contact with the second longitudinal wall, which means that the projecting part is configured on one longitudinal wall and makes contact with the opposing longitudinal wall. In this way, channels that are essentially separated from one another can be provided inside the flat tube.

In a further preferred embodiment, the flat tube exhibits two curved end sections. At least one end section is preferably bent through at least 180 degrees, in order to cause the two longitudinal walls to be arranged essentially parallel in relation to one another. The second end section can also be bent in some other way, in order to close the flat tube; for example, each of the end areas of the basic material can be bent partially about a given angle in the course of the manufacturing process before being joined together at this point.

In a further preferred embodiment, a plurality of projecting parts is configured from the material of the longitudinal wall on a longitudinal wall.

In a further preferred embodiment, projecting parts are configured on both longitudinal walls from the material of the longitudinal walls. In this case, in a further preferred embodiment, all the projecting parts make contact with the opposing longitudinal wall in each case. It is possible in this way to achieve a situation in which the flat tube, in the manufactured state, is configured with a plurality of chambers that are essentially separated in relation to one another.

In this case, the distances between the projecting parts can be selected in such a way that the finished flat tube exhibits channels with an essentially constant cross-sectional area.

In a further preferred embodiment, it is also possible to configure the projecting parts so that they do not make contact with the opposing longitudinal wall, but with a further projecting part arranged on the opposing longitudinal wall.

In a further preferred embodiment, at least one projecting part, preferably a plurality of projecting parts, and especially preferred all the projecting parts, exhibits an essentially symmetrical profile. This means that the projecting part exhibits an axis of symmetry running essentially perpendicular to the plane of the longitudinal wall, in relation to which the projecting part is of essentially axially symmetrical configuration.

In a further preferred embodiment, the flat tubes exhibit a depth between 0.5 mm and 5 mm, preferably between 0.8 mm and 4 mm, and especially preferred between 1 mm and 3 mm. Each of these depths depends on the actual applications in the heat exchangers to be manufactured.

In a further preferred embodiment, at least one wall exhibits a wall thickness between 0.05 mm and 0.8 mm, preferably between 0.07 mm and 0.6 mm and—especially preferred—between 0.1 mm and 0.5 mm. The corresponding projecting parts are preferably adapted depending on this wall thickness, in which case account must also be taken in particular of process engineering requirements.

The present invention also relates to a process for the manufacture of a multi-channel flat tube for a heat exchanger. In this case, a projecting part with a predetermined profile is produced in one process stage from a strip of material by means of a first forming unit and a second forming unit acting together with the first forming unit.

In a further process stage, the profile of the projecting part is modified by means of a third forming unit and a fourth forming unit acting together with the third forming unit.

The expression “modification of the profile” is understood to denote that predetermined geometrical modifications are made to the projecting part and/or its cross section.

The expression “forming unit” is understood to denote an arrangement which acts on the material to be processed in such a way that it is modified, at least locally.

The forming units in question are preferably rollers that are capable of rotating in relation to one another. The first and the second forming units are thus embodied preferably as contra-rotating upper and lower rollers, between which the material to be processed is arranged. In the case of the third and fourth forming units, too, the units in question are corresponding rollers, between which the material to be processed is arranged. The rollers are preferably embodied in such a way that one roller is limited by lateral edges of the other roller, in order in this way to prevent broadening of the strip of material to be worked in the course of the forming process.

In a further preferred embodiment, the rollers exhibit an essentially cylindrical profile.

It would also be possible, however, instead of rollers, to provide two opposing supports, between which the material is pressed and/or pulled.

The change in the profile in at least one process stage preferably involves a reduction in its height and/or width. Preferably both the height and the width of the projecting part are reduced in the course of this process stage. It is possible in this way to achieve the situation in which the outside of the flat tube is made level in the area of the projecting part, which means that a depression is reduced in this area.

The profile of the projecting part is preferably further modified in at least one further process stage. In this case, the height and/or the width of the profile is preferably reduced in turn. Preferably a number of consecutive process stages is provided, in which the profile of the projecting part is continually modified, in conjunction with which this modification in each case involves at least the reduction of the width or the height of the profile. These process stages serve the purpose in each case—as mentioned above—of achieving the greatest possible levelness of the external surface of the flat tube profile in the area of the projecting part.

The profile of the projecting part is modified preferably in at least four process stages, and especially preferred in at least six process stages. Too few process stages would lead to the risk of the material to be processed not being able to withstand the necessary extensive reshaping, possibly resulting in cracking and the like. The number of process stages is restricted in the upward direction by the required efficiency, both in terms of the manufacturing costs and in terms of the time input.

In a further preferred process, pre-centering of the projecting part is undertaken in a further process stage. This is achieved preferably by means of a pre-drawing operation.

The rotating rollers, through which the material is passed, preferably exhibit an essentially constant distance in relation to one another. The situation in which the material for processing exhibits an essentially constant wall thickness and/or gauge is achieved in this way. The material of the roller is preferably matched to the material for processing in such a way that the diffusion of material particles is prevented.

The width of the strip of material is preferably reduced in at least one process stage. The material is supplied to the rollers in the form of strips with predetermined dimensions. The expression “width of the strip of material” is understood to denote its extension in the direction of the axis of the roller. By adopting this procedure, it is possible to achieve the configuration of the projecting part in a particularly advantageous manner in each case. In a further preferred embodiment, the width of the strip of material remains constant in at least one process stage. In these process stages, a modification of the form of the projecting part is achieved essentially without the use of further material from the area surrounding the projecting part.

A plurality of projecting parts is preferably formed from the strip of material. For this purpose, the required quantity of additional material can preferably be obtained by reducing the length of the strip in a first process stage.

The projecting parts in this case are preferably configured at predetermined distances in relation to one another. The projecting parts are preferably selected in such a way that the flat tube produced in this way essentially exhibits a plurality of channels of essentially identical cross section.

Different projecting parts are preferably subjected to different forming steps in at least one process stage. The intention in this case is for a particular projecting part to be adapted already in respect of its form, whereas a further projecting part is only formed or a projecting part already receives its final form, whereas a further projecting part is still adapted in respect of its form in an intermediate stage.

Under certain circumstances, it is possible in this way to arrive at the situation in which a plurality of projecting parts are manufactured with a small number of reshaping stages in such a way that preformed projecting parts or projecting parts that have already been formed in advance are not adapted further in respect of their shape.

A curved section is preferably produced in a further process stage. A curve of 180 degrees is preferably produced in order to arrange the longitudinal walls in this way so that they lie essentially parallel in relation to one another.

Further advantages and embodiments can be appreciated from the accompanying drawings.

In the drawings:

FIG. 1 depicts a representation of the process according to the invention for the production of a projecting part;

FIG. 2 a depicts a representation of the forming units according to the invention for the manufacture of a projecting part;

FIG. 2 b depicts a representation of the forming units for the purpose of modifying the profile of the projecting part;

FIG. 2 c depicts a representation of the forming units for the purpose of further modifying the profile of the projecting part;

FIG. 3 depicts a representation intended to illustrate the manufacturing process for the production of an even number of projecting parts;

FIG. 4 depicts a flat tube produced by the process represented in FIG. 3;

FIG. 5 is a figure provided to illustrate the manufacture of a flat tube with an odd number of projecting parts;

FIG. 6 depicts a flat tube manufactured by a process according to FIG. 5;

FIG. 7 depicts a flat tube according to the invention in a first embodiment;

FIG. 8 depicts a flat tube according to the invention in a second embodiment;

FIG. 9 depicts a flat tube according to the invention in a third embodiment;

FIG. 10 depicts an enlarged representation of a projecting part for the purpose of illustrating the geometrical relationships; and

FIG. 11 depicts a flat tube according to the invention for the purpose of illustrating the geometrical relationships.

The individual process stages of a process according to the invention for the production of a projecting part are depicted in FIG. 1. The individual process stages are identified with the Arabic numerals 1 to 6. The lower-case letters a) to f) in each case designate the width of the material, that is to say the strip of material, during the manufacturing process. The upper-case letters A to F designate the end points of the strip of material.

Attention is drawn to the fact that the process depicted in FIG. 1 shows only one possible variant of the process according to the invention. According to the invention, other process stages may also be proposed, or individual process stages may be omitted.

The reference designation L designates the center line, and preferably the axis of symmetry of the produced projecting part 9 a to 9 f. In the optional process stage 1 a, pre-centering of the projecting part 9 a is undertaken by means of a pre-drawing operation. This is particularly advantageous if the projecting parts and/or the ribs need to be produced with large heights H_(A) to H_(F).

In process stage 2, the strip of material and/or the strip 7 is reshaped in the indicated area Z. For this purpose, the forming units in each case, that is to say preferably the rollers, exhibit a bead-like form. The overall width b of the strip 7 is produced by the production of the projecting part 9 b in process stage 2, in conjunction with which the overall width b is smaller than the overall width a, and respectively the overall width a′ in process stages 1 and 1 a.

The height H_(B) produced in process stage 2 represents the maximum height H_(max) of the projecting part 9 b, which is reduced even further, at least in part, in the course of further process stages.

In stages 2 to 6, the development of the neutral fiber in the area Z remains almost constant. This means that, in the area Z, essentially the same quantity of material is always supplied respectively to the forming units and to the rollers. This is achieved through a corresponding design of the forming stages in each case in steps 2 to 6 by retaining the overall widths of the strips in each case.

The widths of the strips b to f thus remain essentially constant in process stages 2 to 6. In order to keep the overall strip widths b to f constant, the strip of material 7 is preferably retained with suitable tools at each of the end points B to F.

Essentially only one reshaping of the projecting part 9 thus takes place during process stages 2 to 6. In particular, both the height H and the width of the projecting part 9 decrease, and the flanks 25 in each case follow a steeper path. The radius of curvature at the tip of the projecting part 9 a to 9 f in each case is reduced in the course of the process. This means that the material that is economized by a reduction in the height and the width is essentially added by the fact that the surface of the depression 11 is constantly reduced underneath the projecting part.

To put it another way, the width of the strip between the starting point 33 and the end point 34 preferably remains essentially constant during process stages 2 to 6. During process stages 5 and 6, a closure of the projecting part and/or the depression 11 must be achieved underneath the projecting part 9, which means that the flanks 29 of the projecting part are pressed against one another in each case. For this purpose, the material 7 in the area of the projecting part is enclosed essentially completely by the corresponding areas of the forming units.

Alternatively, in process stage 5, the projecting part that is still open in process stage 4 can also be closed by folding together, gathering or pinching. The height H_(D) and/or H_(E) will not be significantly reduced in a procedure of this kind, however, but rather the overall width of the strip. In this case, steps would also have to be taken to counteract the danger of scratching between the pinching tools, in addition to which no ideally reduced rib external cavity 11 will also be obtained.

It is also possible to permit a change in the width of the strip in the area Z, moreover, in at least one of the process stages 3 to 6, which means that the width of the strip b to f will also not remain constant, at least in part, in the process stages 3 to 6. If this variant procedure is adopted, material and/or strip material can flow back into the width of the strip in conjunction with compression of the projecting part, that is to say from the area of the projecting part.

One possible consequence is that too little material will be available to close the external cavity 11 in subsequent process stages, or that more material will need to be pre-drawn in the first stages. In this case, increased thinning of the strip of material 7 and a greater risk of cracking can also occur. The necessary rib height cannot be achieved under certain circumstances, furthermore, and the process will become more sensitive overall in relation to fluctuations in the characteristics of the strip material.

A final height H_(F), which is smaller than the height H_(E) in process stage 5, is achieved in process stage 6 depicted here. At the same time, the area 11, which is still present in process stage 5, is essentially closed, and the smooth outer profile according to the invention is accordingly achieved.

The strip width and/or the overall width of the strip e is also not reduced any further, which means that the strip width f and the strip width e are essentially the same.

FIG. 2 a depicts the forming units for the implementation of the process according to the invention, which comprise an upper roller 21 and a lower roller 22. Arranged between these rollers is the flat tube material and/or the strip of material 7, which is drawn through the rollers by the rollers in this way. The lower roller 22 exhibits a processing projecting part 25, and the upper roller 21 exhibits a depression adapted to the processing projecting part 25 in respect to its form. It would also be possible, on the other hand, to provide the upper roller with a projecting part and the lower roller with a depression.

The depression 26 and the processing projecting part 25 are adapted to one another in such a way that the material can be passed between them with a predetermined gauge and/or thickness S.

FIG. 2 a depicts the pair of rollers 21, 22 at the processing stage 2 according to FIG. 1, which means that the processing projecting part 25 and the depression 26 are so adapted that the resulting projecting part exhibits the height H_(B).

Gaps 13 a and 13 b are provided between the upper roller 21 and the lower roller 22. During the first process stage, material from the strip continues to be drawn into the area of the upper roller.

FIG. 2 b depicts the pair of rollers for the process stage 4. In this case, the depression 26 is designed in such a way that the projecting part achieves the indicated height H_(D). The lower roller 22 here no longer exhibits a processing projecting part. In the meantime, the gaps 13 a and 13 b between the upper roller 21 and the lower roller 22 have been reduced in terms of their width compared with the arrangement illustrated in FIG. 2 a. The lower roller 22 is designed, for example, according to the strip width b of process stage 4 according to FIG. 1.

The strip of material and/or the strip runs against the lower roller during compression. In conjunction with this, the widths of the strip must accordingly be kept essentially constant and/or as constant as possible, as soon as the height H_(B) according to FIG. 2 a is achieved, in order to ensure that no area of the strip flows out of the area of the projecting part into the level area 7 b of the strip.

The arrangement for process stage 6 represented in FIG. 1 is depicted in FIG. 2 c. In this case, the lower roller 22 also no longer exhibits a processing projecting part, and only the upper roller 21 continues to exhibit a depression 26. This depression is adapted in such a way that the final height H_(F) of the projecting part 9 is produced.

In addition to the process stage depicted in FIG. 2 c, the gap widths 13 a and 13 b are selected with minimum values, which means that material and/or the strip must be enclosed completely by the two rollers 21 and 22, so that the projecting part 9 can be reshaped in such a way that the area 11 beneath the projecting part 9 can be closed essentially completely and a smooth outside (in this case the underside) of the material 7 is also produced in the area of the projecting part 9 in this way.

FIG. 3 depicts the process in the case in which a plurality of projecting parts—more precisely an even number of projecting parts—requires to be produced. The individual process stages are identified here with the reference designations I to VIII.

In a first optional stage I, a cavity 31 is produced by means of suitably adapted upper and lower rollers, that is to say rollers which exhibit a processing projecting part and a depression, as depicted in FIG. 2. The production of this cavity is particularly advantageous if the projecting parts to be produced are required to exhibit a comparatively large initial height H_(B).

Two projecting parts 9 a and 9 b are produced in process stage II. An upper roller with a corresponding depression and a lower roller with an appropriately adapted processing projecting part are preferably used for this purpose. It is also possible, however, to utilize a lower roller without a processing projecting part in this process stage.

The width of the strip is reduced from a strip width a in process stage I, to a strip width b in process stage II, and to a strip width c in process stage III. It is also possible, however, to undertake only a reshaping of the projecting parts 9 in process stage III, which in this case means keeping the strip width c essentially constant in relation to the strip width b.

In process stage IV, two further projections 9 c and 9 d are produced by appropriately adapted upper and lower rollers. For this purpose, the strip width c in process stage III is reduced to the strip width d in process stage IV. The lower roller preferably exhibits processing projecting parts for this purpose in the area of the new projecting parts to be produced.

The projecting parts lying further to the inside and then the projecting parts lying further to the outside are preferably produced initially in conjunction with the production of the projecting parts. This is advantageous because it permits material from the outer areas of the strip of material to be used in each case to produce the new projecting parts, and it prevents material from the areas of other, already produced projecting parts from being drawn in. It is also possible, however, to provide and/or to produce a plurality of projecting parts in place of the projecting part depicted here. The process stages depicted in FIG. 3 are also only illustrated by way of example. It would also be possible in exactly the same way to provide significantly more process stages, as well as a plurality of reshaping processes.

The reshaping of the individual projecting parts already depicted in FIG. 1 again takes place in process stages VI to VIII, in conjunction with which once again—as depicted in FIG. 1—the flanks are steeper and the radii of curvature at the tip of the projecting part are smaller, and the heights and widths of the projecting parts are reduced in each case. The entire strip widths, such as f, g and h, are kept essentially constant in this case, as already explained with reference to FIG. 1.

Process stage IV can also be supplemented by further process stages, in order to produce additional projecting parts and/or ribs.

Depicted in FIG. 4 is a flat tube, which can be manufactured by the process outlined in FIG. 3. The flat tube 1 is produced in its cross section by a process of reshaping the strip illustrated in FIG. 3 under reference VIII. In conjunction with this, the strip is bent through 180 degrees in an area between the projecting parts 9 a and 9 b and, in addition, at the end areas in each case, in order to produce the curved areas 18 and 19 in this way. The reference designations 14 and 15 in this case relate to the resulting longitudinal walls, which are arranged essentially parallel to one another.

By further forming processes, for example cold roll forming, the projecting parts 9 a to 9 d can be arranged in such a way that they make contact with the opposing wall in each case (the wall 15 in the case of the projecting parts 9 b and 9 d, and the wall 14 in the case of the projecting parts 9 a and 9 c).

The projecting parts 9 a to 9 d and/or their end areas are preferably soldered to the opposing longitudinal wall in each case. The two bent end areas 18 and 19 are similarly soldered to one another in such a way as to provide a tight joint. A flat tube with five channels in total is achieved by producing the four projecting parts 9 a to 9 d depicted here.

Process stages I to VIII for producing a flat tube with an odd number of projecting parts, in this case more specifically three projecting parts, are represented in FIG. 5. Here, too, reference designation 41 relates to an essentially level and/or smooth strip of material, in other words a flat strip, exhibiting the width a.

A projecting part 9 a is produced in process stage II—similar to that produced in process stage II in FIG. 3. This projecting part is reshaped in process stage III, in conjunction with which the strip width a is reduced initially to the width b in this process stage, and is in turn reduced to the width c, that is to say the width c is smaller than the width b, and the width b is smaller than the width a.

Two further projecting parts 9 b and 9 c are produced in process stage IV. The production of the individual projecting parts 9 a and respectively 9 b and 9 c is transposed in this process, which means that, whereas the first reshaping operation has already taken place in the case of the projecting part 9 a, sections 9 b and 9 c were produced first in this instance. The strip width d in this case is further reduced in relation to the strip width c. In this variant, too, the internal projecting parts are preferably formed initially, followed by the external projecting parts.

The three projecting parts 9 a, 9 b and 9 c are subjected to further forming in process stage V. The width of the strip remains largely constant here, that is to say the strip width e essentially corresponds to the strip width d.

A further reshaping process of the kind described above takes place in process stage VI, that is to say the height of the individual projecting parts 9 a, 9 b and 9 c is reduced, as is their width; the flanks are of a steeper execution for this purpose, and the radii of curvature at the tip of the projecting parts are accordingly smaller.

The width of the projecting parts is reduced even further in a further process stage VII, before being closed finally in process stage VIII. The individual strip widths e, f, g and h essentially remain constant in conjunction with this. Corner folds 42 a and 42 b are formed by bending in the final process stage following process stage VIII. These two corner folds result in the production of a further projecting part, and corner folds are in fact capable of being produced in several process stages.

Depicted in FIG. 6 is a flat tube, which is produced from the lower strip depicted in FIG. 5. Unlike the embodiment depicted in FIG. 4, the end sections in this case are not arranged in the area of the curves 17 or 18, but in the central area. Expressed in precise terms, the components in question here are the folds 42 a and 42 b that are bent upwards in each case. These are welded and/or soldered to one another and as such make a further projecting part available.

In this embodiment, too, the individual projecting parts 9 a to 9 c and the projecting part produced by the end folds 42 a and 42 b make contact with the opposing longitudinal wall of the flat tube in each case. A flat tube with five channels is produced in this embodiment, too. The process (process stages I-VIII) illustrated in FIG. 5 can be utilized generally for flat tubes with an odd number of projecting parts, whereas the process depicted in FIG. 3 preferably finds an application for flat tubes with an even number of projecting parts. The design of the end folds 42 a, 42 b according to FIG. 6 and/or the end folds 18, 19 according to FIG. 4, on the other hand, is achievable in particular in a previously disclosed way and is largely unaffected by the number of projecting parts.

Illustrated in FIG. 7 is a flat tube according to the invention, in which the individual dimensions serve as an illustration. The representation of the smooth and/or level external surface of the flat tube, that is to say the representation of the minimized surface 11 beneath the projecting part 9, has been dispensed with here in the interests of better understanding. In addition, the flanks of the projecting part are represented in a non-compressed state.

Reference designation a relates to the distance of the ribs along a longitudinal wall. Reference designation K denotes the distance between two neighboring ribs, which under certain circumstances form a chamber. Reference designation T denotes the thickness of the flat tube.

In the embodiment illustrated here, the thickness T preferably lies between 1 mm and 3 mm. The chamber and/or the size of the channel has been selected here so that it is about half as large as the distance between the ribs a (distance of the projecting parts). The minimum distance between the ribs in this embodiment is at least twice as large as the width T. The minimum chamber size and/or channel size is accordingly at least as large as, or larger than the thickness T.

In the embodiment shown in FIG. 8, projecting parts 9 which make contact with the longitudinal wall 15 are applied only on the longitudinal wall 14. In this case, the rib distance a essentially corresponds to the chamber size and/or the channel size K. In this embodiment, too, the minimum rib distance a is greater than the thickness T, which is also determined by the manufacturing process in this case. Because the rib distance a corresponds to the channel size K, the channel size is also at least twice as large as the thickness T of the flat tube.

In the embodiment depicted in FIG. 9, the individual projecting parts 9 do not make contact with the opposing longitudinal wall 14 and/or 15 in each case, but with projecting parts 9 that are themselves applied to the opposing longitudinal wall. This means that the ends of the projecting parts make contact with one another more or less at the center of the flat tube. In this case, too, as in the embodiment according to FIG. 8, the size of the channel K is essentially equal to the rib distance a. In this case, however, the minimum rib distance is larger than or equal to the thickness T of the flat tube. This also applies to the chamber size and/or the channel size K.

In a further embodiment (not illustrated here), it is also conceivable to execute the individual projecting parts in such a way that—unlike the embodiment depicted in FIG. 9—they are slightly displaced laterally in relation to one another, so that they do not make contact at their ends in each case, but rather on their lateral surfaces, as a result of which an increased connection surface can be achieved.

FIG. 10 depicts an enlarged representation of a projecting part 9 according to the invention, in which its dimensions are indicated individually. In order to achieve the end form illustrated in FIG. 10, between four and ten process stages are envisaged, in which the projecting parts in each case are reshaped. The number of process stages to be used is determined by the height H_(F) to be reached, the wall thickness and the strip thickness t and the material characteristics. If it is wished to produce a number of projecting parts and/or ribs, a far larger number of process stages may be required, however.

In FIG. 10, the reference designation rf denotes the upper radius of curvature, X denotes the width of the projecting part at its tip, Y the width of the projecting part 9 at its base, RF the radius of curvature at the base of the projecting part and r_(D) the radius of curvature of the depression 11. The individual sizes are partially correlated to one another.

The boundaries indicated below are the result of extensive soldering and reshaping trials. In the course of these trials, the parameters were matched to one another according to a predetermined system, and the results were utilized for the boundaries represented here.

The upper radius of curvature rf in this embodiment lies between 0 and the wall thickness t, that is to say it is smaller than the wall thickness t. The lower radius of curvature RF is smaller than twice the wall thickness t. The upper width X of the projecting part lies between one-and-a-half times and two times the wall thickness t. The lower width Y of the projecting part lies between two times and two-and-a-half times the wall thickness t, which means that the upper width X is smaller than the lower width Y, which is also the outcome of the forming process.

The height of the projecting part H_(F) lies between the wall thickness t and ten times this wall thickness t. The lower radius of the depression r_(D) is also smaller than the wall thickness t. The wall thickness t lies between 0.05 mm and 0.8 mm, preferably between 0.1 mm and 0.7 mm, and especially preferred between 0.1 mm and 0.5 mm. This means that the expression “an essentially smooth external profile” is understood to denote a profile of the kind which is produced by radii of curvature r_(D) that are smaller than the wall thickness t. FIG. 11 depicts a view from above of the flat tube according to the invention. This exhibits only a single projecting part and/or rib 9, and it is accordingly divided into two channels.

The proportion of the tube width b to the tube height H lies between 10 and 30, and preferably between 10 and 24.

The size of the chamber and/or the size of the channel lies between one third of the width of the tube and one half of the width of the tube.

The height of the projecting part h_(F) preferably lies between three times the wall thickness and eight times the wall thickness. The lower radius of curvature rd is found to be less than 0.75 times, and preferably smaller than or equal to 0.5 times the wall thickness t. In this embodiment, the wall thickness lies between 0.05 mm and 0.6 mm, preferably between 0.1 mm and 0.4 mm, and especially preferred between 0.15 mm and 0.3 mm. In conjunction with this, a depression 11 remains on the outside of the flat tube, which exhibits a surface area of less than 0.01 mm², and preferably of less than 0.006 mm². This represents a considerable improvement compared with the prior art.

The depression 11 illustrated in FIG. 10 exhibits a surface area of less than 0.1 mm², and preferably less than 0.07 mm², which also represents a considerable improvement compared with the prior art.

Thanks to this considerable reduction in the surface area of the depression 11, the flat tube, as mentioned by way of introduction, can be soldered far more easily to the base of the tube, and a tight connection can be achieved at far lower cost. 

1. A multi-channel flat tube for a heat exchanger, in particular for a motor vehicle, having a first longitudinal wall, a second longitudinal wall, which lies substantially parallel to the first longitudinal wall, and at least one curved end section, in conjunction with which a projecting part is configured on at least one longitudinal wall from the material of the longitudinal wall on the inside facing a fluid flow in the interior of the flat tube, wherein the longitudinal wall is essentially level on its outside facing away from the fluid in the area of the projecting part.
 2. The flat tube as claimed in claim 1, wherein the projecting part configured on a longitudinal wall is in contact with the second longitudinal wall.
 3. The flat tube as claimed in claim 1, wherein it exhibits two curved end sections.
 4. The flat tube as claimed in claim 1, wherein a plurality of projecting parts is configured on a longitudinal wall from the material of the longitudinal wall.
 5. The flat tube as claimed in claim 1, wherein projecting parts are configured on both longitudinal walls from the material of the longitudinal walls.
 6. The flat tube as claimed in claim 1, wherein a plurality of projecting parts, and preferably all the projecting parts, make contact with the opposing longitudinal wall in each case.
 7. The flat tube as claimed in claim 1, wherein at least one projecting part on one longitudinal wall makes contact with a projecting part on the opposing longitudinal wall.
 8. The flat tube as claimed in claim 1, wherein at least one projecting part exhibits an essentially symmetrical profile.
 9. The flat tube as claimed in claim 1, wherein the flat tube exhibits a depth between 0.5 mm and 5 mm, preferably between 0.8 mm and 4 mm, and especially preferred between 1 mm and 3 mm.
 10. The flat tube as claimed in claim 1, wherein at least one projecting part exhibits a height H_(F) between three times and eight times a wall thickness of the flat tube, and in particular between four times and six times a wall thickness of the flat tube.
 11. The flat tube as claimed in claim 1, wherein at least one wall and preferably the whole of the flat tube exhibits a wall thickness between 0.05 mm and 0.8 mm, preferably between 0.07 mm and 0.6 mm and especially preferred between 0.1 mm and 0.5 mm.
 12. The flat tube as claimed in claim 1, wherein at least one projecting part exhibits a depression with a radius of curvature r_(D), which is smaller than or equal to a wall thickness of the flat tube, and is preferably smaller than or equal to 75% of a wall thickness of the flat tube.
 13. A device for the exchange of heat having at least one flat tube as claimed in claim
 1. 14. A process for the manufacture of a multi-channel flat tube for a heat exchanger with the following process stages: Production of a projecting part with a predetermined profile from a strip of material by means of a first forming unit and a second forming unit acting together with the first forming unit; Modification of the profile of the projecting part by means of a third forming unit and a fourth forming unit acting together with the third forming unit.
 15. The process as claimed in claim 12, wherein the forming units are rollers that are capable of rotating in relation to one another.
 16. The process as claimed in claim 1, wherein, in conjunction with the modification of the profile of the projecting part, its height and/or width is reduced.
 17. The process as claimed in claim 1, wherein the profile of the projecting part is further modified in at least one further process stage.
 18. The process as claimed in claim 1, wherein the profile of the projecting part is modified in at least four, and preferably in at least six process stages.
 19. The process as claimed in claim 1, wherein pre-centering of the projecting part is undertaken in a process stage.
 20. The process as claimed in claim 1, wherein the rotating rollers exhibit axes of rotation that are parallel to one another.
 21. The process as claimed in claim 1, wherein the width of the material strip is reduced in at least one process stage.
 22. The process as claimed in claim 1, wherein the width of the material strip remains essentially constant, and in particular remains constant, in at least one process stage.
 23. The process as claimed in claim 1, wherein a plurality of projecting parts is configured from the material strip.
 24. The process as claimed in claim 1, wherein the projecting parts are configured at predetermined distances in relation to one another.
 25. The process as claimed in claim 1, wherein the projecting parts are subjected to different forming steps in at least one process stage.
 26. The process as claimed in claim 1, wherein a curved section is produced in a further process stage. 